DirtonSoil
Where’s the Beach?
Moving the Cape Hatteras Lighthouse
(From: http://www.its-about-time.com/htmls/pbis/dig_te_ls3/ls3_s_3_2.pdf)
The Cape Hatteras Lighthouse was built in 1870. During this time, people did not have the technology or knowledge to fully understand the forces of erosion. So building the lighthouse 457 m (1500 ft) from the water seemed reasonable. For over a hundred years, the lighthouse warned ships away from dangerous waters in a part of the ocean called the “Graveyard of the Atlantic.” However, after 129 years, the lighthouse itself was in danger of falling victim to the sea. Coastal erosion had worn away about 396 m (1300 ft) f beach. The lighthouse now sat within 46 m (150 ft) of the very waters it had warned so many sailors to stay away from. In 1999, the lighthouse was moved 884 m (2900 ft) back to save it from falling into the ocean.
The Cape Hatteras lighthouse is located on the Outer Banks of North Carolina’s barrier islands. Barrier islands are found all along the eastern coast of the United States, parallel to the mainland’s shoreline. They are also found along many other shorelines around the world.
These long, sandy islands protect the mainland from the winds and pounding waves of the sea. The islands are constantly moving, eroding in one place and building up in another. This is the result of waves, currents, winds, storms, and a rising sea level.
Barrier islands are often in need of protection from the forces of erosion. After all, if they were to disappear, mainland shorelines would be defenseless from the seas. Their best defense is the dunes. These dunes are anchored in place by the deep roots of dune plants. Most beach communities work hard to protect their dunes. Signs are often posted, asking people to stay off the dunes and not pick the dune plants. Still, barrier islands are eroding at incredible rates. Because of their beauty and recreational value, barrier islands are popular places to build homes and visit. Often, people build along these beaches without considering erosion.
The beach erosion problem has many causes:
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Building houses and hotels near the ocean;
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A rapid rise in average ocean levels;
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The gradual sinking of coastal land;
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Efforts to reduce erosion that have not worked, and instead have increased it, and
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Global warming, which is expected to speed up the rise in sea level.
Yet erosion is not all bad. Without erosion, there would be no beaches, dunes, barrier islands or bays. Bays are bodies of water found between barrier islands and the mainland. They are productive nurseries for many marine organisms.
Simple solutions that cause more problems
Some cities, such as Miami Beach in Florida, are built right up to the cliffs above the beach. In Miami Beach, people noticed that the cliffs were beginning to erode. The ocean was getting closer to the buildings. The city reinforced the cliffs with sea walls. But the sea walls reflected wave energy more rapidly to the sea. This only made erosion occur more rapidly. It also kept the sand that normally erodes from the cliffs from depositing on the beaches. For both reasons, sea walls were not a good solution to Miami Beach’s erosion problem.
Landowners thought that building a rock wall perpendicular to the beach, about 50-200 yards out from the shore, might slow the erosion. Ocean currents would hit the rock wall, which would slow them down. As water slows down, it carries less sediment. This type of rock wall is called a groin. However, in Miami Beach, the groin caused the ocean to deposit more sand near one end of the groin and very little at the other end of the groin. There are many such groins along the New Jersey coast and they, too, are not a good solution to the erosion caused by the ocean.
One way to restore beaches is to pump sand into them. This solution is called “beach nourishment”. The sand is taken from deep waters or dredging projects. Although expensive, this solution seems to work for a while. The problem is that the same forces that removed the sand in the first place will remove the sand again. On the Middle Atlantic coast, sand needs to be pumped into the beaches about every five years.
Take a break water!
Another possible solution is building offshore to reduce the strength of the waves before they hit the beaches. Breakwaters are long heaps of rocks dumped parallel to the shore. These rock walls slow down the waves. However, many people consider them to be unattractive and unnatural looking.
Breakwaters built beneath the water offer many of the same benefits without spoiling the view. A submerged breakwater acts like a coral reef, causing the waves to break before they reach the shore. However, how and where to build them has not been worked out.
